Should macular erythema reactions be counted as positive allergic patch-test reactions?

Background: Positive allergic patch-test results are generally described as erythematous papules, vesicles, or a spreading reaction with crust and ulceration. This description excludes milder reactions, including macular erythema. Objective: Our aim was to investigate the prevalence and relevance of reactions graded as macular erythema at Mayo Clinic. Methods: Between January 2001 and June 2004, patients suspected of having allergic contact dermatitis were patch-tested with our institution's standard patch test, a screening series of 68 to 72 allergens. In total, 2,823 patients were patch-tested with 193,530 allergen applications. Reactions were interpreted with the North American Contact Dermatitis Group scale, including and excluding reactions graded as macular erythema. Irritant reactions were excluded from calculations. For this study, scores for current, questionable, and past relevance were combined. Results: On day 5, with the exclusion of reactions graded as irritant, 7,274 allergen applications were associated with reactions, including 3,082 (42.4%) that were graded as macular erythema. Of the macular erythema reactions, 2,430 (78.8%) were graded as relevant. The rate of reaction in our patients was 2.2% if macular erythema was excluded, 3.8% if all macular erythema reactions were included, and 3.4% if only those macular reactions deemed relevant were included. Conclusion: Patch-test reactions rated as macular erythema are common and may be of clinical relevance. For the purposes of patient education, they should not be disregarded. Consideration should be given to including these reactions when reporting patch-test results.